Review Optimize upgrade guidance for relevance in 8.8

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Description

There is currently a separate upgrade guide for Optimize. During review, it was unclear whether this guide still applies to upgrades to Camunda 8.8.

Some feedback suggested that:

• the separate Optimize upgrade guide may have been required for earlier versions (for example, 8.7), but
• it may no longer be applicable or necessary for 8.8.

This issue is to review the Optimize upgrade documentation and determine:

• whether a separate Optimize upgrade guide is still required for 8.8,
• whether the content needs to be updated or simplified, or
• whether the guidance should be removed completely or merged into the main upgrade flow.